MAGELLANIC CLOUDS

Evening Post, Volume CX, Issue 102, 27 October 1925, Page 3

MAGELLANIC CLOUDS

QUAINT NATIVE LEGENDS

"A STAR AS BIG AS A SACK"

VISIBLE OVER THE SOUTH POLE,

Tlie expression, the " Clouds o£ Magellan," was used originally to indicate the two bright nebulous objects in the neighbourhood of the south celestial pole, now known to astronomers as th\i Nubccuhie Major and Minor, and also the pear-shaped dark mass adjacent to the Southern Cross, known as the Coal Sack. These three remarkable objects, although named after the navigator and adventurer Fernando Magellan, who observed them in 1520, had been previously noticed by residents uorth of tho Equator. The larger cloud was known to Al Sufi, a Persian astronomer of the 10th century, Marco Polo saw the clouds toward the close of the 13th century, and writing of his discovery, made a sketch of the largo cloud, which he quaintly described as being "a, star as big as a sack."

The Indians of South America first directed v the attention of Magellan towards the luminous masses, states "Sig-euot-h" in the Melbourne "Argus." lie narrates that the wise'men of the tribes of Patagonia taught that the light clouds were composed of the plumes of ostriches killed by the ancestors of the tribes in the chase. According to Vie traditions of the Australian aborigines, the larger of the light clouds represents a male native companion, and the smaller its female mate, while . the dark cloud, the coal sack, represents an emu, Tchingal, which, being pursued by Bunya, a native armed with spears, turned on and chased him. Bunya, alarmed for his safety, threw away his spears, clambered up, and took refuge at the top of a tree, represented by part of the Southern Cross. For- his cowardice, he was transformed into an opossum, and was killed later by Berm-borm-gl, two brothers, famed for their skill and courage- in the ■ chase. . They are now commemorated by the stars Alpha, and Beta Centanri, the pointer!) to the cross; After-slaying Bunya, the brothers attacked and killed" Tchingal j the spear which passed through ' the emu's body being indicated by the stars Alpha, at the foot, and Beta, the- second star in the cross. Bunya was immortalised, and he shines as Gamma, the star at-the summit of the Cross.

COMPOSITION OF CLOUDS,

Sir John Herschel, while Astronomer Royal at the Cape of Good Hope, from 1835 to 1838, devoted much time to the study of the composition of the luminous clouds. He found them to be aggregations on a vast scale of every'"variety of cosmical product, and stated that' when examined ' through powerful telescopes their constitution, and especially that of Nubecula Major, was found to be of astonishing complexity. He drew up a preliminary catalogue of. 1163 stars, nebulae, and clusters included in them. He i referred to the nubeculae as being the most conspicuous features of the barren south polar heavens, and stated that round the lesser cloud especially, the sky was oppressively desolate, the access to it on all sides being .through a desert. He enthusiastically referred to one of the inmates of the larger cloud, the "great looped nebula," which he compared to an assemblage of loops, Jthe complicated windings of which make it one of the most extraordinary objects that the heavens present. In her work, "The llerschels and Modern Astron omy," Miss Agnes Clerke, who alsn made observations at the Cape, states that this , nebula resembles a shining strip of cellular tissue hung up against the sky, the tracery of nebula being closely followed by a tracery of stars, "A most wonderful combination, as Herschel exclaimed in contemplating it." Commenting, upon the statement that the access to the lesaer cloud appears to be through a desert, Proctor suggested the . probability that the regions had been drained to form part of the Nebeculae.

In 1890 and 1891 Mr. Russell, of Sydney Observatory, succeeded in obtaining very fine photographs of the Nebeculae. According to Miss Clerke, these contained an extraordinary revelation. Both objects came out as gigantic spirals, their miscellanepus contents being arranged according to the dictates of a prevalent though unexplained cosmical law. The Nebecula Major' shows as a double vortex, and the extent of its outlying portions, invisible except to the camera, is at least eight times that of the central mass, but conforming to the same helical lines. In an article on the "Milky Way," published recently. Professor Forbes states, referring to the Conl Sack, that either the light oJ the Milky Way is there obscured by a black cloud among the stars, or else there is a, hole going right through the Milky Way. LIGHT AND DARK NEBULAE.

, There are scattered over the heavens, in addition to the light nebulae, numbers of dark clouds of "matter, which wholly or partially obscure the light of stars and stellar matter behind them. At one time it was seriously believed that these assumed vacancies, including the Coa! Sack, wero openings through to abysmal darkness of unoccupied space. Sit John Hersehcl's investigations at the Cnpe. showed, however, that the Coal Sack, although v dark patch to the. naked eye, was not devoid of stars, visible through powerful .telescopes. 1 Photographs taken since at southern observatories confirm these observations. Professor Barnard, when at Mount Wilson Observatory, niado a, systematic study of these dark patches, and obtained lniudreds of beautiful photographs. Even a casual glance at some of these photographs reveals masses of dark matter projected against lighter backgrounds, clearly nrii.ifesliti<j that tfio dark Mnatter is cons'dcrably nearer to U3 than the lighter background. In his article, l'mCessor Forbes writes: "There is another reason why this Southern Hemisphere of 'lie Milky Way is the more interesting. It is only there that the Magellanic clouds can' be seen, two glowing cloudlets, like dotached fragments of the Milky Way. Ii) those regions the galaxy is resplendent' It no lnnjer resembles a mere wash of white paint upon the celestial vault. It suggests an assemblage of luminous clouds,, and may well give the beholder a fancy that tho Creator has taken great haudfuls of universes, like snowballs, made of myriads of stars, and has hurled them into tho ring of light, there to spread out and encroach on one another, while some parts of the ring seem to have escaped the bombardment, leaving blank spaces: and two throws seem to have missed their aim entirely and formed tin; Magellanic clouds." Reluctant though one may be. to disturb this poetical imagery," it is probable that the Magellanic clouds did, at. one period of time, form part of the Milky Way. MIGRATING CLOUDS. Professor Moultou, joint author with Chamberlain of the "Planctesimal Theory," lately directed attention to tho fact that K. E. Wilson, at the South American branch ot 11 in Lick Observatory, lias found that the radial vdoci-

tics of the nebulae in the Magellanic clouds, which are bright enough for measurement, show rapid recession of all these objects, the average speed being over 150 miles a second, and states that this suggests that theso aggregations of stars have velocities, with respect to our own galaxy, of a higher order than the average internal velocities of our galaxy. Dingle, in his Modern Astrophysics," published last year, after reviewing at length the evidence available on the matter, concludes: "The .most probable explanation of the Magellanic Clouds is that they are systems of the same kind as soma of those which build up our galaxy. ' It may bo that they once inhabited tho same regions but from one cause or other left the populous plains and took wings for the southern skies. If their present velocities are even approximately equal to those which they have had in tha past, they .must have been associated with the large system at no very remold period, as cosmic history runs." Professor Hurlow Shapley, after investigation, and using Wilson's values for velocity in line of light, has recently found that the lesser cloud was in or near tha Milky Way 1,900,000,000 years ago. This would not he a "very remote period," as cosmic history runs. Recently Professor Shapley • has also investigated the distances and' dimensions of the clouds. The method of determination was one well known to astronomers, depending on the luminosity period of relation of Ccpheid variable' stars, lie deduces the distance of tha larger cloud to bo 11.1,850 light years, and of the smaller cloud i 04,280 light years. If these figure? bc'runUiplied by six, and twelve cyphers be added to tha product, the totals will give approximately the distances in British.mileage. A light year approximates to six billions —i.e., six millions of millions of miles, tho distance which light travels iii'oue year. „ .